Systems and methods for on line collecting and resuspending cellular-rich blood products like platelet concentrate

ABSTRACT

Systems and methods resuspend cellular-rich concentrates of blood by rocking the separation chamber to create variable agitation forces within the separation chamber. The systems and methods also add resuspension fluids to aid the resuspension.

FIELD OF THE INVENTION

The invention generally relates to blood processing systems and methods.

BACKGROUND OF THE INVENTION

Today blood collection organizations routinely separate whole blood intoits various therapeutic components, such as red blood cells, platelets,and plasma.

One separation technique that is in widespread use today uses a multipleblood bag system. The bag system includes a primary blood bag and one ormore transfer bags, which are integrally connected to the primary bag bytubing. The technique collects from a donor a single unit (about 450 ml)of whole blood in the primary blood bag. The donor is then free toleave.

The donor's whole blood later undergoes centrifugal separation withinthe primary bag into red blood cells and plasma rich in platelets. Theplasma rich in platelets is expressed out of the primary bag into atransfer bag, leaving the red blood cells behind. The plasma rich inplatelets then undergoes further centrifugal separation within thetransfer bag into a concentration of platelets and plasma poor inplatelets. The plasma poor in platelets is expressed from the transferbag into another transfer bag, leaving the concentration of plateletsbehind.

Using multiple blood bag systems, all three major components of wholeblood can be collected for therapeutic use. However, the yield for eachcomponent collected is limited to the volume of the components that arecontained in a single unit of whole blood. Furthermore, because redblood cells are retained, United States governmental regulationsprohibit collecting another unit of whole blood from the donor until sixweeks later.

Certain therapies transfuse large volumes of a single blood component.For example, some patients undergoing chemotherapy require thetransfusion of large numbers of platelets on a routine basis. Multipleblood bag systems simply are not an efficient way to collect these largenumbers of platelets from individual donors.

On line blood separation systems are today used to collect large numbersof platelets to meet this demand. On line systems perform the separationsteps necessary to separate a concentration of platelets from wholeblood in a sequential process with the donor present. On line systemsestablish a flow of whole blood from the donor, separate out the desiredplatelets from the flow, and return the remaining red blood cells andplasma to the donor, all in a sequential flow loop.

Large volumes of whole blood (for example, 2.0 liters) can be processedusing an on line system. Due to the large processing volumes, largeyields of concentrated platelets (for example, 4×10¹¹ plateletssuspended in 200 ml of fluid) can be collected. Moreover, since thedonor's red blood cells are returned, the donor can donate whole bloodfor on line processing much more frequently than donors for processingin multiple blood bag systems.

Nevertheless, a need still exists for further improved systems andmethods for collecting cellular-rich concentrates from blood componentsin a way that lends itself to use in high volume, on line bloodcollection environments, where higher yields of critically neededcellular blood components like platelets can be realized.

SUMMARY OF THE INVENTION

The invention provides systems and methods for resuspendingcellular-rich concentrates of blood.

The systems and methods that embody the features of the inventioncomprise a separation chamber with a motor mechanism for moving theseparation chamber. The motor mechanism is operable in a first mode formoving the separation chamber about an axis to create centrifugal forceswithin the chamber. The motor mechanism is also operable in a secondmode for rocking the separation chamber to create variable agitationforces within the separation chamber.

The systems and methods include a control mechanism that is operable ina separation mode and in a resuspension mode.

In the separation mode the control mechanism operates the motor in itsfirst mode, rotating the separation chamber, while (i) conveying a bloodinto the chamber for separation in response to the centrifugal forcesinto a cellular-rich concentrate and a cellular-poor component, and (ii)conveying at least a portion of the cellular-poor component from theseparation chamber, leaving the cellular-rich concentrate behind in theseparation chamber.

In the resuspension mode, the control mechanism operates the motor inits second mode, rocking the separation chamber, to suspend thecellular-rich concentrate within the separation chamber in response tothe agitation forces.

In a preferred embodiment, the control mechanism is further operable ina collect mode for conveying resuspended cellular-rich concentrate fromthe separation chamber.

In a preferred embodiment, during the resuspension mode, the controlmeans conveys a resuspension fluid for mixing with the cellular-richconcentrate within the separation chamber.

In a preferred embodiment, before switching to the resuspension mode,the control means removes at least a portion of the residual fluidvolume present in the separation chamber to intensify the agitationforces during subsequent rocking.

The invention is especially well suited for resuspending a platelet-richconcentrate collected during an on line blood separation process.

As used in this Specification, the term "on line blood separationprocess" refers to a blood separation system or method that (i)establishes communication between a source of blood and a flow path;(ii) draws a blood volume from the source into the flow path; and (iii)maintains communication with the blood source for at least a portion ofthe time that the blood volume undergoes separation within the flowpath.

As used in this Specification, an "on line blood separation process" canseparate the blood volume either in a continuous manner or in aninterrupted manner. However, an "on line blood separation process"maintains communication between the flow path and the blood source forat least a portion of the time the separation process occurs within theflow path, regardless of specific timing or sequencing of the separationprocess itself.

As used in this Specification, an "on line blood separation process" caninclude external or internal valves or clamps to interrupt flow withinthe path to or from the blood source. However, in the context of thisSpecification, such valves or claims do not break the communicationbetween the blood source and the flow path. Instead, the valves orclamps control fluid flow within the path while maintainingcommunication between it and the blood source.

The invention may be embodied in several forms without departing fromits spirit or essential characteristics. The scope of the invention isdefined in the appended claims, rather than in the specific descriptionpreceding them. All embodiments that fall within the meaning and rangeof equivalency of the claims are therefore intended to be embraced bythe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a three stage blood processing systemthat embodies the features of the invention;

FIG. 2 is a plan side view of a blood processing assembly thatintegrates two separation elements of the system shown in FIG. 1;

FIG. 3 is a top view of the two element assembly shown in FIG. 2;

FIG. 4 is a perspective view of the two element assembly shown in FIG.2, being partially wrapped upon a centrifuge rotor for use and inassociation with the remaining separation element of the system;

FIG. 5 is a side view, with portions broken away and in section, of acentrifuge for rotating the assembly shown in FIG. 4;

FIG. 6 is a partially diagrammatic view of a multi-stage two needleblood processing system that incorporates the separation elements shownin FIG. 4;

FIG. 7 is a diagrammatic view of the two needle blood processing systemshown in FIG. 6; and

FIG. 8 is a diagrammatic view of a process for controlling the returnand retention of platelet-poor plasma in the system shown in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows in diagrammatic form a multiple stage blood processingsystem 10 that embodies the features of the invention.

In use, the system 10 draws whole blood (WB) from a donor, while addinganticoagulant. The system 10 ultimately separates the anticoagulated WBinto three end products.

The first end product is red blood cells (RBC). The second end productis a platelet-poor component, which is commonly called platelet-poorplasma (PPP). The third end product is a resuspended, leukocyte-depletedplatelet concentrate (RES-LDPC).

The system 10 returns RBC to the donor. The system 10 retains RES-LDPCfor long term storage and subsequent therapeutic use. The system 10returns a portion of the PPP to the donor. According to one aspect ofthe invention, the system 10 retains the rest of the PPP for variousprocessing purposes and for long term storage for therapeutic purposes.

The system 10 employs three separation stages to create these three endproducts.

In the first separation stage, the system 10 directs anticoagulated WBfrom the donor into a first separation element 12. The first element 12separates the whole blood into RBC and an intermediate product, whichconstitutes a platelet suspension.

This platelet suspension is typically plasma rich in platelets, and itis commonly referred to as platelet-rich plasma (PRP). However, as usedin this Specifications the term "platelet suspension" is not limited toPRP in the technical sense. The term "platelet suspension" is intendedto encompass any suspension in which platelets are present inconcentrations greater than in whole blood, and can include suspensionsthat carry other blood components in addition to platelets.

In the second separation stage, the system 10 directs PRP into a secondseparation element 14. The second element 14 reduces the number ofleukocytes from the PRP, creating another intermediate product, whichconstitutes leukocyte depleted PRP (LDPRP).

As used in this Specification, the term "leukocyte depleted" does notdenote that all or substantially all the leukocytes have been removed.The term is intended to more broadly indicate only that the number ofleukocytes have been reduced by some active separation process.

In the illustrated and preferred embodiment, the system 10 diverts aportion of PRP exiting the first element 12 away from the secondseparation element 14. This diverted flow of PRP is recirculated backinto the first separation element 12. The recirculated PRP joins the WBentering the first separation element 12.

In the third separation stage, the system 10 directs LDPRP into a thirdseparation element 16. The third element 16 separates LDPRP into anotherintermediate product, which consists of leukocyte depleted plateletconcentrate (LDPC) and PPP.

As used in this-Specification, the term "platelet concentrate" is notlimited to PC in the technical sense. The term "platelet concentrate" isintended to encompass a volume of platelets that results after a"platelet suspension" (as that term is used in this Specification)undergoes a subsequent separation step that reduces the fluid volume ofthe platelet suspension.

In the illustrated and preferred embodiment, the system 10 returns someof the PPP to the donor during the processing period. The system 10retains the rest of the PPP during the processing period.

The system 10 uses the retained PPP in various transitional processingmodes.

In one transitional mode, the system 10 adds retained PPP to LDPC. ThePPP resuspends the LDPC, creating the RES-LDPC end product. The PPPserves as storage medium for the RES-LDPC during long term storage.However, RES-LDPC can be used for therapeutic use without long termstorage.

In another transitional mode, the system 10 uses the retained PPP as ananticoagulated fluid to rinse resident RBC from the system 10 afterprocessing for return to the donor.

In still another transitional mode, the system 10 uses the retained PPPas an anticoagulated fluid to keep fluid lines open and patent duringtemporary interruptions in processing activity.

In still another transitional mode, the system 10 recirculates theretained PPP to mix with WB entering the first separation element 12.The mixing of retained PPP with WB improves the separation of RBC andPRP in the first element 12.

The system 10 collects the remaining retained PPP for therapeuticpurposes, with or without long term storage.

EXAMPLE 1

The exact constitution of the various blood products created by thesystem 10 during process varies according to the particular physiologyof the whole blood donor. Furthermore, as above indicated, theterminology used in this Specification is not intended to berestrictive.

Still, this Example is provided to describe for purposes of illustrationthe constitution of the blood products that can be obtained from ahealthy donor.

A typical healthy donor has a WB hematocrit (Hct) of between 40% (0.4)and 50% (0.5) before donating WB. The hematocrit indicates the volume ofRBC per unit volume of WB.

The healthy donor's WB also contains about 250,000 platelets for eachmicroliter (μl) of plasma.

After separation in the first separation device 12, a portion of theplasma accompanies the RBC that is returned to the donor. As a result,the remaining platelet suspension (PRP) contains a higher concentrationof platelets than WB.

In PRP obtained from the typical donor, there are about 350,000 to400,000 platelets for each μl of plasma.

The number of platelets per ml of PRP can also be accurately estimatedusing the following general expression: ##EQU1## where Platelets_(PRP)is the concentration (in number per μl) of platelets in the donor's PRP;

where Platelets_(WB) is the concentration (in number per μl) ofplatelets in the donor's WB before donation; and

where Hct is the predonation hematocrit of the donor's WB.

Essentially all the platelets carried in PRP entering the third separateelement 16 are there separated from the plasma. The resulting LDPC takesthe consistency of a thick fluid-poor "paste" that carries an extremelyhigh concentration of platelets (approximately 30,000,000 to 40,000,000platelets per μl).

The LDPC is preferably resuspensed in about 200 ml of PPP to formRES-LDPC. The resulting RES-LDPC contains about 2,000,000 platelets perml resuspended in this fluid volume.

In the illustrated and preferred embodiment, the system 10 comprises,once sterilized, a sterile, "closed" system, as judged by the applicablestandards in the United States. Furthermore, the system 10 remains"closed" during processing. This assures that the longest authorizedstorage intervals can be used for the components collected.

As will soon be apparent, the system 10 also lends itself to on lineand/or continuous blood separation processes.

The system 10 having the benefits of the invention can be variouslyconstructed.

In the illustrated and preferred embodiments, the system 10 separatesblood components in both the first and third elements 12 and 16 usingcentrifugation techniques. Still, it should be appreciated that otherseparation techniques could be used for these purposes.

For example, the system 10 can employ centrifugal separation techniquesin conjunction with the first element 12 and employ membrane separationtechniques in conjunction with the third element 16. Such two stageprocessing techniques using a combination of centrifugal and membraneseparation are disclosed in Schoendorfer U.S. Pat. No. 4,851,126 andKruger et al. U.S. Pat. No. 4,680,025.

In the particular preferred embodiment shown in FIGS. 2 to 4, the system10 integrates the first and third elements 12 and 16 into a singlecentrifugal processing chamber assembly 18. Alternatively, the first andthird elements 12 and 16 could comprise physically separate processingchambers.

In the illustrated and preferred embodiment (best seen in FIG. 4), achamber assembly 18 is formed of two sheets of flexible medical gradeplastic joined along their outer edge by a first peripheral seal 20 (seeFIG. 2, also).

A second interior seal 22 divides the assembly 18 into a firstprocessing compartment 24 and a second processing compartment 26.Although part of an integral assembly 18, each processing compartment 24and 26 actually serves as a separate and distinct separation element.

More particularly, the first compartment 24 comprises the firstprocessing element 12. Here, centrifugal forces separate whole bloodinto RBC and PRP.

The second compartment 26 comprises the third processing element 16.Here, centrifugal forces separate LDPRP into LDPC and PPP.

Further details of the chamber assembly 18 are set forth in copendingU.S. patent application Ser. No. 07/965,088, filed Oct. 22, 1992 andentitled "Enhanced Yield Platelet Collection Systems and Methods." Thisapplication is incorporated into this Specification by reference.

In use, the chamber assembly 18 is wrapped about a rotor 28 of acentrifuge 30 (see FIGS. 4 and 5).

The rotor 28 rotates about an axis 32 to generate centrifugal forces.The centrifugal field extends radially from the axis 32 through eachcompartment 24 and 26. The compartment wall radially spaced farther fromthe axis 32 will be called the high-G wall 34 (see FIGS. 3 and 4). Thecompartment wall radially spaced closer to the axis 32 will be calledthe low-G wall 36.

The assembly 18 establishes a circumferential flow of fluid duringprocessing. That is, the fluid introduced into each compartment 24 and26 during rotation follows a circumferential flow path in thecompartment 24 and 26 about the rotational axis 32.

In response to the centrifugal forces generated in the first compartment24, the higher density RBC move toward the high-G wall 34, displacingthe lighter density PRP toward the low-G wall 36 of the firstcompartment 24. An intermediate layer called the interface forms betweenthe RBC and PRP. The interface constitutes the transition between theformed cellular blood components and the liquid plasma component.

Large amounts of leukocytes populate the interface. When dynamic forceswithin the compartment 24 are not optimized, platelets, too, can settleout of the PRP and onto the interface.

In response to the centrifugal forces generated in the secondcompartment 26, the higher density platelets in the PRP move toward thehigh-G wall 34. They displace the lighter density liquid PPP toward thelow-G wall 36 of the second compartment 26.

The construction and operation of the centrifuge 30 can vary. Furtherdetails of the centrifuge 30 are set forth in U.S. patent applicationSer. No. 07/814,403, filed Dec. 23, 1991 and entitled "Centrifuge withSeparable Bowl and Spool Elements Providing Access to the SeparationChamber". This application is incorporated into this Specification byreference.

Five ports 38/40/42/44/46 open into the compartmentalized areas of theprocessing assembly 18. The ports 38/40/42/44/46 are arrangedside-by-side along the top transverse edge of the respective chamber 24and 26. Three ports 38/40/42 serve the first chamber 24. Two ports 44/46serve the second chamber 26.

The first port 38 comprises a PRP collection port. The second port 40comprises a WB inlet port. The third port 42 comprises a RBC collectionport. The fourth port 44 constitutes a PPP collection port. The fifthport 46 constitutes a LDPRP inlet port.

The first chamber 24 includes a third interior seal 48 (see FIG. 2)located between the PRP collection port 38 and the WB inlet port 40. Thethird seal 48 extends generally parallel to the second interior seal 22and then bends in a dog-leg away from the WB inlet port 40. The dog-legterminates beneath the inlet of the PREP collection port 38. The thirdinterior seal 48 forms a PRP collection region 50 within the firstchamber 24.

The first chamber 24 also includes a fourth interior seal 52 locatedbetween the WB inlet port 40 and the RBC collection port 42. The fourthseal 52 extends generally parallel to the second and third interiorseals 22 and 48 and then bends in a dog-leg away from the RBC collectionport 42. The dog leg terminates near the longitudinal side edge of thefirst chamber 24 opposite to the longitudinal side edge formed by thesecond interior seal 22.

Together, the third and forth interior seals 48/52 form a WB inletpassage 54. Together, the fourth interior seal 52, the second interiorseal 22, and the lower regions of the first peripheral seal 20 form aRBC collection passage 56.

The WB inlet passage 54 channels WB directly from the WB inlet port 40into the flow path at one end of the first chamber 24. WB enters thecircumferential flow path immediately next to the PRP collection region50. Here, the radial flow rates of plasma are greatest, to liftplatelets free of the interface and into the PRP collection region 50.

The RBC collection passage 56 receives RBC at the opposite end of theintended circumferential flow path for WB within the chamber 24. Fromthere, the RBC collection passage 56 channels the RBC back to the RBCcollection port 42.

A ramp 58 (see FIG. 2) extends from the high-G wall 34 of the firstcompartment 24 across the PRP collection region 50. The ramp 58 forms atapered wedge that restricts the flow of fluid toward the PRP collectionport 38.

The ramp 58 also orients the interface between RBC and PRP formed duringseparation for viewing through a side wall of the chamber assembly 18 byan associated interface controller (not shown). The interface controllermonitors the location of the interface on the ramp 58 and varies therate at which PRP is drawn from the chamber 24. This holds the interfaceat a prescribed location on the ramp 58, keeping RBC, white blood cells,and lymphocytes away from the PRP collection port 38.

In the illustrated embodiment, a hinged flap 60 (see FIG. 4) extendsfrom and overhangs a portion of the rotor. The flap 60 is preformed topresent the desired contour of the ramp 58.

Further details of interface control using the ramp 130 are shown inBrown. U.S. Pat. No. 4,834,890, as well as in U.S. patent applicationSer. No. 07/965,088, filed Oct. 22, 1992 and entitled "Enhanced YieldPlatelet Collection Systems and Methods." Both are incorporated intothis Specification by reference.

The second compartment 26 includes a fifth interior seal 62 (see FIG. 2)that extends between the LDPRP inlet port 46 and the PPP collection port44. The fifth seal 62 extends generally parallel to the second seal. 22and then bends in a dog-leg away from the LDPRP inlet port 46 in thedirection of circumferential PRP flow within the second chamber 26. Thedog-leg terminates near the longitudinal side edge of the second chamber26 opposite to the longitudinal side edge formed by the second interiorseal 22.

The fifth interior seal 62, the second interior seal 22, and the lowerregions of the first peripheral seal 20 together form a PPP collectionpassage 64. The PPP collection passage 64 receives PPP at its open endand, from there, channels the PPP to the PPP collection port 44.

In the illustrated and preferred embodiment (see FIG. 3), the low-G wall36 of the first compartment 24 is offset toward the high-G wall 34,tapering into the compartment 24 in the direction of circumferential WBflow. In the illustrated and preferred embodiment (see FIG. 3), thelow-G wall 36 also likewise tapers into the second compartment 26 in thedirection of circumferential PRP flow.

In the illustrated and preferred embodiment (see FIG. 2), the dog legportion of the RBC collection passage 56 and the dog leg portion of thePPP collection passage 64 are both tapered in width to present anenlarged cross section where they open into their respect ire chamber 24and 26. The tapered widths of the passages 56 and 64 are each preferablygauged, relative to the inward radial taper of the low-G wall 36, tokeep the cross sectional area of the RBC collection passage 56 and PPPcollection passage 64 substantially constant.

The control of the cross section areas of the collection passages 56 and64 keeps fluid resistance within the passages 56 and 64 relativelyconstant. It also maximizes the available separation and collectionareas outside the passages 56 and 64. The tapered passages 56 and 64also facilitate the removal of air from the assembly 18 duringpre-processing priming.

The tapering low-G wall 36 in the first compartment 24 also preferablyincludes a stepped-up barrier 66 (see FIGS. 2 and 3) in the region wherethe RBC collection passage 56 opens into the compartment 24. Thestepped-up barrier 66 extends from the low-G wall 36 across the entirechamber 24, as FIG. 2 shows. The stepped-up barrier 66 extends into theRBC mass formed during separation, creating a restricted passage 66between it and the facing high-G wall 34 (see FIG. 3). The restrictedpassage 66 allows RBC present along the high-G wall 34 to move beyondthe barrier 66 for collection by the RBC collection passage 56.Simultaneously, the stepped-up barrier 66 blocks the passage of the PRPbeyond it, keeping the PRP within the dynamic flow conditions leading tothe PRP collection region 50.

Flexible plastic tubing attached to the ports 38/40/42,/44/46interconnects the first and second chambers 24 and 26 with each other,with the second separation element 14, and with pumps and otherstationary components located outside the rotating components of thecentrifuge 30. The flexible tubing is ganged together into an umbilicus70 (see FIGS. 4 to 6).

As FIG. 6 best shows, the non-rotating elements attacked to theumbilicus 70 include the second separation element 14, the phlebotomyneedles 78 and 80 that provide vein access to the donor, and the variouscontainers 80 that provide or receive fluid during processing.

More particularly, the umbilicus 70 connects the WB inlet port 40 andthe RBC collection port 42 of the rotating assembly 18 with stationaryphlebotomy needles 78 and 80. One needle 78 continuously draws WB fromthe donor, while the other needle 80 continuously returns RBC to thedonor. Alternatively, the system 10 could use a single phlebotomy needleto perform both functions in sequential draw and return cycles usingconventional techniques.

The umbilicus 70 also connects the PRP collection port 38 of the firstchamber 24 with the LDPRP inlet port 46 of the second chamber 26, viathe second separation element 14, as FIG. 6 best shows. The secondchamber 26 thereby receives LDPRP through the umbilicus 70 from thefirst chamber 24 (via the second separation element 14) for furtherseparation into, PPP and LDPC. As FIG. 6 also shows, a portion of thePRP exiting the PRP collection port 38 is diverted away from the secondseparation element 14 for recirculation directly back to the WB inletport 40.

The umbilicus 70 also conveys separated PPP from the second chamber 26through the associated PPP collection port 44. A portion of PPP isconveyed by the umbilicus 70 to the donor return needle 80. Anotherportion of PPP is conveyed by the umbilicus to one or more of thecollection containers 81 for retention.

The LDPC remains behind in the second chamber 26 for later resuspensionand collection, as will be described later.

As FIG. 5 shows, in operation, the centrifuge 30 suspends the rotor 28in an upside down position during rotation, compared to the positionshown in FIG. 4.

As FIG. 5 also shows, a non-rotating (zero omega) holder 72 holds theupper portion of the umbilicus 70 in a non-rotating position above therotor 28.

Another holder 74 rotates the mid-portion of the umbilicus 70 at a first(one omega) speed about the rotor 28. Another holder 76 (see FIG. 4)rotates the lower end of the umbilicus 70 next to the assembly 18 at asecond speed twice the one omega speed (the two omega speed), at whichthe rotor 28 also rotates. This known relative rotation of the umbilicus74 and rotor 28 keeps the umbilicus untwisted, in this way avoiding theneed for rotating seals.

The dimensions of the various regions created in the processing chambercan, of course, vary according to the processing objectives. Table 1shows the various dimensions of a representative embodiment of aprocessing assembly 18 of the type shown in FIGS. 2 and 3. Dimensions Athrough F referenced in Table 1 are identified in FIGS. 2 and 3.

TABLE 1

Overall length (A): 191/2 inches

Overall height (B): 2-13/16 inches

First Stage Processing Chamber

Length (C): 101/8 inches

Width (D): 23/8 inches

Maximum Radial Depth in Use: 4 mm

Second Stage Processing Chamber

Length (E): 8-13/16 inches

Width (F): 23/8 inches

Maximum Radial Depth in Use: 4 mm

Port Spacing (center line to center line ): 3/8 inch

In this configuration the RBC collection passage 56 and the PPPcollection passage 64 taper from a width of about 1/4 inch to 1/8 inch.The restricted passage 68 in the first compartment 24 is about 1 mm to 2mm in radial depth and about 1 mm to 2 mm in circumferential length.

In this configuration, when the rotor 28 is rotated at a speed of about3400 RPM, a centrifugal force field of about 900 G's is generated alongthe high-G wall 34 of the chambers 24 and 26.

Alternatively, the system 10 can employ physically separate processingchambers as the first and third elements 12 and 16. Such elements couldthen be usable in association with a commercially available bloodprocessing centrifuge, like the CS-3000® Blood Separation Centrifugemade and sold by the Fenwal Division of Baxter Healthcare Corporation (awholly owned subsidiary of the assignee of the present invention). Thesealternating processing chambers are also disclosed in copending U.S.patent application Ser. No. 07/965,088, filed Oct. 22, 1992 and entitled"Enhanced Yield Platelet Collection Systems and Methods."

In the illustrated and preferred embodiment, the system 10 carries outblood component separation in the second element 14 using filtration.

Still, the second element 14.can use other separation techniques. Thesecond element 14 can separate leukocytes by centrifugation, absorption,columns, chemical, electrical, and electromagnetic means.

In the illustrated and preferred embodiment, the second element 14comprises a filter device 82 that employs a non-woven, fibrous filtermedia 84.

The composition of the filter media 84 can vary. In the illustrated andpreferred, embodiment, the media 84 comprises fibers that containnonionic hydrophillic groups and nitrogen-containing basic functionalgroups. Fibers of this type are disclosed in Nishimura et al U.S. Pat.No. 4,936,998, which is incorporated herein by reference. Filter media84 containing these fibers are commercially sold by Asahi MedicalCompany in filters under the tradename SEPACELL.

Filter media 84 containing these fibers have demonstrated the capacityto remove leukocytes while holding down the loss of platelets.

The system 10 shown in FIGS. 1 to 6 can be readily incorporated into acontinuous single or double needle on line blood processing systems.FIG. 7 shows in diagrammatic form a representative continuous two needleon line processing system 86 that carries out an automated resuspendedplatelet collection procedure employing the features of the invention.

A processing controller 88 operates the two needle system 86 incontinuous collection and return cycles, which occur simultaneously. Asused in this Specification, the terms "continuous" and "simultaneous"are not meant to be limited to sequences that are continuous orsimultaneous only in the quantitative sense. The terms are meant toencompass sequences that, while not absolutely continuous orsimultaneous quantitatively, are "substantially" continuous orsimultaneous in a qualitative sense, when there is no significantoperational or therapeutic difference in terms of the way they operateand the function and result achieved.

In the collection cycle, the donor's WB is continuously supplied throughthe draw needle 78 to the processing compartment 24 (for separation intoRBC and PRP), while continuously conveying PRP from the compartment 24into the filter device 82 (for creating LDPRP), and while continuouslyconveying LDPRP from the filter device 82 into the compartment 26 (forseparation into LDPC and PPP).

During the return cycle, which in the two needle system 86 occurssimultaneously with the collection cycle, the controller 88 continuouslyreturns RBC from the compartment 24 and a portion of the PPP from thecompartment 26 to the donor through the return needle 80.

Throughout the processing period, the circulatory system of the donorremains connected in communication with the system 86 through theneedles 78 and 80.

The controller 88 also continuously retains a portion of the PPP exitingthe compartment 26, diverting it from return to the donor, during theentire period that LDPC is being separated in the compartment 26. Thesystem 86 retains the diverted PPP for long term storage, as well as toaid processing and resuspension of LDPC in the compartment 26 for longterm storage as RES-LDPC.

The system 86 includes a container 90 that holds anticoagulant. Whilethe type of anticoagulant can vary, the illustrated embodiment usesACDA, which is a commonly used anticoagulant for pheresis.

The system 86 also includes a container 92 that holds saline solutionfor use in priming and purging air from the system 86 before processingbegins.

The system 86 also includes one or more collection containers 94 forreceiving RES-LDPC for therapeutic use, with or without long termstorage. The system 86 also includes one (or optionally more) collectioncontainer 96 for retaining PPP during processing. The container 96ultimately can also serve as a long term storage container for retainedPPP.

Under the control of the controller 88, a 10 first tubing branch 98 anda WB inlet pumping station 100 direct WB from the draw needle 78 to theWB inlet port 40 of the first stage processing chamber 24. The WB inletpumping station 100 operates continuously at, for example, 50 ml/min.Meanwhile, an auxiliary tubing branch 102 meters anticoagulant to the WBflow through an anticoagulant pumping station 104.

ACDA anticoagulant can be added to constitute about 9% of the entry WB.Saline dilution fluid can also be added in an amount representing about4% of donor body volume (i.e., 200 ml saline for 5000 ml in bodyvolume).

Anticoagulated WB enters and, fills the first processing chamber 24 inthe manner previously described. There, centrifugal forces generatedduring rotation of the chamber assembly 18 separate WB into RBC and PRP.

The controller 88 operates a PRP pumping station 106 to draw PRP fromthe PRP collection port 38 into a second tubing branch 108.

The processing controller 88 monitors the location of the interface onthe ramp 58. It varies the speed of the PRP pumping station 106 to keepthe interface at a prescribed location on the ramp 58. The controller 88also limits the maximum rate of the variable PRP pumping station 106(for example, 25 ml/min) to be less than the WB inlet pumping station100.

Meanwhile, a third tubing branch 110 conveys the RBC from the RBCcollection port 42 of the first stage processing chamber 24. The thirdtubing branch 110 leads to the return needle 80 to return RBC to thedonor.

The system 86 includes a recirculation tubing branch 112 and anassociated recirculation pumping station 114. The processing controller88 operates the pumping station 114 to divert a portion of the PRPexiting the PRP collection port 38 of the first processing compartment24 for remixing with the WB entering the WB inlet port 94 of the firstprocessing compartment 24.

The controller 88 can control the recirculation of PRP in differentways.

In the illustrated and preferred embodiment, the pumping rate of therecirculation pump 114 is maintained as a percentage (%_(RE)) of thepumping rate WB inlet pump 100 governed as follows:

    %.sub.RE =K*Hct-100

where:

Hct is the hematocrit of the donor's whole blood, measured beforedonation, and

K is a dilution factor that takes into account the volume ofanticoagulant and other dilution fluids (like saline) that are added tothe donor's whole blood before separation.

When the pumping rate of the recirculation pump 114 is maintained at thepredetermined percentage (%_(RE)) of the pumping rate WB inlet pump 100,a surface hematocrit of about 30% to 35% is maintained in the WB entryregion of the first compartment 24. The preferred surface hematocrit inthe entry region is believed to be about 32%.

Keeping the surface hematocrit in the entry region in the desired rangeprovides maximal separation of RBC and PRP.

The value of the dilution factor K can vary according to operatingconditions. The inventor has determined that K=2.8, when ACDA anti,coagulant is added to constitute about 9% of the entry whole bloodvolume, and a saline dilution fluid is added in an amount representingabout 4% of donor body volume (i.e., 200 ml saline for 5000 ml in bodyvolume).

By mixing PRP with the WB entering the first processing compartment 24to control surface hematocrit in the entry region, the velocity at whichRBC settle toward the high-G wall 66 in response to centrifugal forceincreases. This, in turn, increases the radial velocity at which plasmais displaced through the interface toward the low-G wall 64. Theincreased plasma velocities through the interface elute platelets fromthe interface. As a result, fewer platelets settle on the interface.

The remainder of the PRP exiting the first compartment 24 enters thefilter device 82 (by operation of the pumping station 106) for removalof leukocytes. A preferred flow rate of PRP through the filter device 82is in the range of 15 to 30 ml/minute.

The continuous on-line removal of leukocytes from PRP that the inventionprovides does not activate platelets carried in the PRP.

The concurrent recirculation of a portion of the PRP away from thefilter device 82 reduces the overall flow volume load on the filterdevice 82. This, in turn, enhances the leukocyte removal efficiencies ofthe filter device 82.

A fourth tubing branch 118 conveys LDPRP to the LDPRP inlet port 46 ofthe second stage processing chamber. 26. There, LDPRP undergoes furtherseparation into LDPC and PPP, as earlier described.

PPP exits the PPP collection port 44 of the second stage processingchamber 26 through a fifth tubing branch 120. The fifth tubing branch120 joins the third tubing branch 110 (carrying RBC), which leads to thereturn needle 80.

The system 86 includes a sixth tubing branch 122 and an associatedpumping station 124 for continuously retaining a portion of the PPPduring the entire processing period.

The processing controller 88 operates the PPP retaining pumping station124 throughout the period that separation occurs within the compartment26 to continuously divert a prescribed portion of the PPP exiting thePPP collection port 44 away from the third tubing branch 110. The sixthtubing branch 122 continuously conveys the diverted PPP to thecollection container 96 for retention.

As before stated, the remainder of the PPP exiting the secondcompartment 26 enters the third branch 110, where it joins the RBC forreturn to the donor by operation of the PPP return pump station 116.

The processing controller 88 controls the flow rate of the pumpingstation 124 to retain the desired proportional volume of PPP separatedin the second chamber 26. The system 86 returns the remaining PPP to thedonor.

In the preferred embodiment, the controller 88 incorporates a PPPretention control process 132 (see FIG. 8) that governs the rate atwhich PPP should be retained (expressed in ml/min) during the processingperiod to collect the volume of PPP desired by the end of the processingperiod. The control process not only takes into account the physicaloperating parameters of the system 86, but it also takes into accountthe physiology and comfort of the individual donor.

As FIG. 8 shows, the control process 132 receives as input the donor'sweight; the donor's platelet count (before donation); the desiredplatelet yield; and the targeted system efficiency. The systemefficiency is expressed as the percentage of the platelets processedthat are ultimately collected as LDPC.

Taking these parameters into consideration, the control process 132determines the total WB volume that should be processed to obtain thedesired platelet yield.

From the total WB volume, the control process 132 derives the total PPPvolume. The plasma volume is derived by multiplying the total WB volumeby (1.0-Hct), where Hct is expressed in decimal form (e.g., 0.4 insteadof 40%).

The control process 132 also receives as input the amount of PPP theoperator wants to retain during processing. The control process 132first compares the desired PPP retention volume to the maximum volume ofPPP that, under applicable governmental regulations, can be retained. Inthe United States, for example, the Food and Drug Administration limitsthe volume of plasma that can be collected from a donor during a givenprocedure to 600 ml for donors with a body weight less than 175 pounds,and 750 ml from a donor with a body weight equal to or greater than 175pounds.

If the desired PPP retention volume does not exceed the maximumallowable retention volume, the control process 132 subtracts thedesired PPP volume from the total PPP volume to derive the PPP returnvolume. Otherwise, the control process 132 generates an error signal,informing the user that less PPP must be retained.

The control process 132 uses the donor's hematocrit (Hct) and theselected anticoagulant ratio to set a WB flow rate the donor should beable to tolerate. A look up table can be empirically prepared tocorrelate WB flow rates with these factors.

Alternatively, the user can select a nominal WB flow rate based uponexperience (say, 50 to 60 ml/min). The user can then make on lineadjustments as necessary during processing based upon the observedresponse of the donor.

Based upon the WB processing volume and the selected anticoagulantratio, the control process 132 determines the volume of anticoagulantthat will be mixed with WB during processing.

The control process 132 adds together the total WB processing volume andthe total anticoagulant volume (plus any dilution fluids, if added) todetermine the total fluid volume that will be processed. By dividing thetotal fluid volume by the WB flow rate, the control process 132calculates the total processing time.

Based upon dividing the desired PPP retention volume by the derivedprocessing time, the control process 132 derives the rate at which thePPP retention pump 124 must be operated.

The control process 132 also determines the effect of the PPP retentionrate upon the rate at which the donor's receives citrate in the portionof PPP that is returned to the donor. The control process adjusts thederived PPP retention rate as necessary to avoid a citrate return ratethat is higher than a preset, physiologically relevant value.

Based upon the total volume of anticoagulant and the type of theanticoagulant, the control process. 132 determines the total volume ofcitrate that will be mixed with WB.

The proportion of citrate contained in anticoagulants is known. Forexample, ACDA anticoagulant contains 21.4 mg of citrate for each ml ofsolution.

Based upon the proportion of PPP that will be returned to the donor, thecontrol process 132 derives the rate at which the system will infuse thecitrate into the donor. The control process 132 derives the citrateinfusion rate in terms of the amount of citrate (in mg) the donorreceives with the returned PPP per unit of donor body weight (in kg) perunit of processing time (in minutes).

The control process 132 compares the derived citrate infusion rate to anominal citrate infusion rate, which is also expressed in mg citrate perkg body weight per minute of processing time. The nominal citrateinfusion rate represents a predetermined maximum rate that citrate canbe infused in a typical donor without causing donor discomfort and othercitrate-related reactions. The control process 132 in the illustratedand preferred embodiment sets the nominal citrate infusion rate at 1.2mg/kg/min, which is based upon empirical data.

As long as the targeted PPP retention rate results in a citrate infusionrate that is equal to or less than 1.2 mg/kg/min, the controller 88 isfree to adjust the operating parameters of the system 86 as necessary tomaximize the component yields and processing efficiencies.

However, if a targeted PPP retention rate results in a citrate infusionrate that exceeds 1.2 mh/kg/min, the controller 88 adjusts theprocessing parameters to lower the citrate infusion rate.

The control process 132 shown in FIG. 8 can be expressed in various waysin terms of a series of simultaneous equations that, when solved, derivethe operating parameters listed above. The equations can be solvedrecursively during processing to take into account changes in Hct andplatelet counts in the donor's WB.

The continuous retention of PPP serves multiple purposes, both duringand after the component separation process.

The retention of PPP serves a therapeutic purpose during processing. PPPcontains most of the anticoagulant that is metered into WB during thecomponent separation process. By retaining a portion of PPP instead ofreturning it all to the donor, the overall volume of anticoagulantreceived by the donor during processing is reduced. This reduction isparticularly significant when large blood volumes are processed.

By continuously diverting PPP away from the donor throughout theseparation process, the donor realizes this benefit continuouslythroughout the processing period, provided that the nominal citrateinfusion rate is not exceeded. The monitoring function that controlprocess 132 performs assures that this benefit will be obtained.

Also the retention of PPP during processing keeps the donor's plateletcount higher and more uniform during processing. This is because thedonor receives back less fluid volume during the processing period,thereby reducing the dilution of whole blood undergoing processing.

EXAMPLE 2

This Example demonstrates the results obtained by operation of thecontrol process 132 shown in FIG. 8 in connection with a plateletcollection procedure for a representative donor.

In this Example, the donor is assumed to have a body weight of 125 lbs(56.3 kg). The donor is also assumed to have a preprocessing Hct of 40%and a preprocessing platelet count of 250,000 per μl.

In this Example, the desired platelet yield for the process is 4.0×10¹¹; and the desired system efficiency is 90%. ACDA anticoagulant is usedat a WB-to-anticoagulant ratio of 9%.

Based upon the above assumptions, the control process derives 2.0 L asthe total WB volume that must be processed. The total volume of PPPassociated with this WB volume is 1200 ml.

Based upon the 9% anticoagulant ratio, the control process 132 derives180 ml as the volume of anticoagulant that will be added. The totalprocessing volume is therefore 2180 ml. The total citrate volume is3.852 g.

The user sets 60 ml/min as the nominal WB inlet flow rate. At this rate,the processing time will be 36.3 minutes.

The user seeks to ultimately retaining 500 ml of PPP during processing,which is well short of the prescribed maximum for the donor's bodyweight. With a processing time of 36.3 minutes, the PPP retention pumpmust be operated at a rate of 13.8 ml/min throughout the process tocollect the desired PPP volume of 500 ml.

The remaining 700 ml will be returned to the donor. This means that thedonor will receive only about 58% (7/12^(th)) of the total anticoagulantvolume that would have been received, if the system 86 retained no PPP.

Moreover, when 500 ml of PPP is retained, the total fluid volumereturned to the donor is just 3/4 of the total drawn volume. In a singleneedle system, each return cycle would take less time and allow anoverall higher blood flow rate.

The control process 132 derives the citrate infusion rate by firstdetermining the volume of citrate that the returned PPP will carry,which is 2.247 g (7/12^(th) of 3.852 g). The control process 132 thendivides the returned citrate volume by the donor's body weight (56.3 kg)and by the processing time (36.3 min) to obtain a citrate return rate of1.1 mg/kg/min.

The control process 132 determines that the citrate return rate is lessthan the nominal 1.2 mg/kg/min. The PPP retention pump 124 can therebybe operated at 13.8 ml/min without anticipating adverse donorcitrate-related reactions.

The system 86 also derives processing benefits from the retained PPP.

ALTERNATIVE RECIRCULATION MODE

The system 86 can, in an alternative recirculation mode, recirculate aportion of the retained PPP, instead of PRP, for mixing with WB enteringthe first compartment 24.

In this mode, the system 86 opens clamps C6 and C7 to convey retainedPPP from the container 96 through a PPP recirculation branch 134 (seeFIG. 7) and associated pumping station 136 into the recirculation branch112.

The controller 88 controls the pumping station 136 in the same mannerdescribed for pumping station 114 to mix retained PPP with the incomingWB entering the first compartment 24.

KEEP-OPEN MODE

Should WB flow be temporarily halted during processing, the system 86enters a "keep-open" mode. In this mode, the system 86 draws upon theretained volume of PPP as an anticoagulated "keep-open" fluid.

More particularly, the system controller 88 closes clamps C1 and C2,opens clamp C3, and operates the pump 116 to direct a volume of the PPPfrom the container 96 through a keep open tubing branch 126, whichcommunicates with the WB tubing branch 98. The anticoagulant present inthe PPP keeps the WB tubing branch 98 open and patent until the flow ofanticoagulated WB resumes.

The system controller 88 keeps the return needle 80 open and patent byintermittently closing clamp C3 and opening clamp C2 to provide a keepopen flow of anticoagulated PPP through the return needle 80.

Use of PPP as a keep-open fluid avoids the need to introduce additionalanticoagulant from container 90 for this purpose.

RINSE-BACK MODE

The system 86 also enters a "rinse-back" mode at the end of theseparation process. In this mode, the system 86 draws upon the retainedvolume of PPP as a "rinse-back" fluid.

More particularly, the system controller 88 stops the flow of WB throughthe tubing branch 98 by closing clamp C4. The system controller 88closes the clamp C2, opens clamp C3, and operates the pump 16 to directa volume of the collected PPP into the first separation compartment 24through tubing branches 122, 120, 126 and 98. The flow of PPP resuspendsand purges RBC from the compartment 24 for return to the donor throughthe return branch 110.

Because PPP, and not saline, is the rinse-back fluid, downstreamcomponent separation through the filter device 82 and the secondcompartment 26 can continue without interruption during the rinse-backmode. The PPP volume used for rinse-back purposes ultimately returns,after separation in the first compartment 24 and flow through the secondcompartment 26, to the source PPP retention container 96.

RESUSPENSION MODE

The system 86 also operates in a resuspension mode to draw upon aportion of the retained PPP to resuspend LDPC in the second compartment24 for transfer and storage as RES-LDPC in the collection container(s)94.

In this mode, the system controller 88 closes clamps C2, C3, and C5,while opening clamp C1. The controller 88 operates the pump 124 toconvey a volume of retained PPP through the PPP collection port 44 intothe second compartment 26. This returned PPP volume mixes with andresuspends LDPC in the second compartment 26.

Preferably, during the resuspension period, the compartment 26 is notrotated at high speeds. Instead, as PPP is conveyed into the secondcompartment 26, the rotor 28 slowly oscillates the assembly 18 first inone rotational direction and then in an opposite rotational direction.The oscillation creates constantly changing acceleration or agitationforces that aid the mixing and resuspension process within the secondcompartment 26.

Also, a substantial portion of the fluid volume residing with the LDPCin the second compartment 26 is preferably drawn away before introducingthe resuspension volume of PPP. The controller 88 operates the pump 124to convey this residual fluid volume from the second compartment 26 intothe PPP retention container 96.

In the illustrated and preferred embodiment, the second chamber 26contains about 40 ml of PPP at the end of the processing period. About20 ml of the residual fluid volume is conveyed away before resuspendingthe LDPC.

The second compartment 26 is therefore about half empty of residualfluid when the resuspension process begins. This fluid-depletedcondition concentrates the volume of LDPC to intensify the accelerationforces generated when the compartment 26 is oscillated. This furtherenhance the mixing and resuspension process.

In the illustrated and preferred embodiment, about 20 ml of PPP isreturned and used as a resuspension fluid. After a predetermined mixingperiod, the system controller 88 closes clamp C1, opens clamp C5, andoperates the RES-LDPC pumping station 128. This conveys the RES-LDPCvolume out the PPP collection port 44 through a RES-LDPC collectiontubing branch 130 into the container(s) 94 for storage.

In a preferred implementation, the resuspension mode constitutes aseries of sequential resuspension batches. In each batch, the residualfluid volume of the second compartment 26 is depleted by about 20 ml,and the assembly 18 is oscillated, and a prescribed aliquot of about 20ml PPP is conveyed into it.

Following a set mixing period, a volume of LDPC that is resuspended isconveyed out of the second compartment 26 and into the container(s) 94.These sequential batches repeat, until all the volume of LDPC issuspended and conveyed as RES-LDPC into the collection container(s) 94.

At the end of the resuspension process, a resuspension volume of PPP(typically about 200 ml) resides with the RES-LDPC to serve as a storagemedium. Typically, about 4.0×10¹¹ platelets are suspended in this fluidvolume.

The remaining volume of retained PPP is stored in the container 96 forsubsequent therapeutic use.

The system 86 thereby boosts the yield of usable therapeutic componentsduring a given collection procedure.

In a single needle collection system (not shown) that embodies thefeatures of the invention, a return cycle does not occur simultaneouslywith a collection cycle. Instead, the single system repeatedly togglesbetween a collection cycle and a return cycle.

During a given collection cycle, WB is drawn through the single needle,and the separated RBC and a portion of the separated PPP are temporarilypooled in reservoirs. When a preselected volume of RBC is pooled in thismanner, the associated controller switches to a return cycle. In thereturn cycle, the WB flow from the donor is suspended, while the pooledRBC and PPP are returned to the donor through the same single needle.

In a single needle system, processing can continue uninterrupted throughthe compartment 24, filter device 82, and the compartment 26 during areturn cycle by collecting a quantity of WB in a reservoir upstream ofthe compartment 24 during the collection cycle. The single needle systemthen draws WB from the reservoir for processing during a return cycle.

A single needle system also retains a portion of the PPP exiting thecompartment 26, diverting it from pooling and return to the donor,during the entire period that LDPC is being separated in the compartment26. The retained PPP is used for the same purposes in a single needlesystem as in a two needle system.

The chamber assembly 18, the associated containers, and theinterconnecting tubing branches associated with the system can be madefrom conventional approved flexible medical grade plastic materials,such as polyvinyl chloride plasticized with di-2-ethyl-hexylphthalate(DEHP).

Preferable, the container(s) 94 intended to store the resuspended LDPC,are made of polyolefin material (as disclosed in Gajewski et al U.S.Pat. No. 4,140,162) or a polyvinyl chloride material plasticized withtri-2-ethylhexyl trimellitate (TEHTM). These materials, when compared toDEHP-plasticized polyvinyl chloride materials, have greater gaspermeability that is beneficial for platelet storage.

Various features of the inventions are set forth in the followingclaims.

I claim:
 1. A method for collecting a resuspended platelet-richconcentrate comprising the steps of(a) rotating a separation chamberabout an axis to create centrifugal forces within the chamber, while:(i)continuously conveying a suspension of platelets into the separationchamber for separation in response to the centrifugal forces into aplatelet-rich concentrate and a platelet-poor component, (ii)continuously conveying the platelet-poor component from the separationchamber, leaving the platelet-rich concentrate behind in the separationchamber, and (iii) continuously collecting a predetermined portion ofthe platelet-poor component in a reservoir, (b) terminating rotation ofthe separation chamber and the conveyance of platelet suspension intothe separation chamber when a desired yield of platelet-rich concentrateoccupies the chamber, (c) removing about one-half of the fluid volumeoccupying the chamber by conveying platelet-poor component from theseparation chamber to the reservoir, (d) rocking the separation chamber,with about one-half of its fluid volume removed, to create intensifiedvariable agitation forces within the separation chamber, (e) returningplatelet-poor component from the reservoir to the chamber, while rockingthe separation chamber, in a volume sufficient to essentially replacethe fluid volume removed in step (c), to thereby at least partiallyresuspend platelet-rich concentrate within the separation chamber inresponse to the agitation forces, (f) conveying a partial volume ofplatelet-rich concentrate, resuspended in returned platelet-poorcomponent, from the separation chamber to a collection container,leaving a remaining volume of platelet-rich concentrate occupying theseparation chamber, and repeating steps (c) to (f) in succession untilsubstantially all of the platelet-rich concentrate is resuspended withreturned platelet-poor component and is conveyed to the collectioncontainer.
 2. A method for collecting a resuspended platelet-richconcentrate comprising the steps of(a) rotating a separation chamberabout an axis to create centrifugal forces within the chamber, while:(i)continuously conveying a suspension of platelets into the separationchamber for separation in response to the centrifugal forces into aplatelet-rich concentrate and a platelet-poor component, (ii)continuously conveying the platelet-poor component from the separationchamber, leaving the platelet-rich concentrate behind in the separationchamber, and (iii) continuously collecting a predetermined portion ofthe platelet-poor component in a reservoir, (b) terminating rotation ofthe separation chamber and the conveyance of platelet suspension intothe separation chamber when a desired yield of platelet-rich concentratecomprising about 4.0×10¹¹ platelets occupies the separation chamber, (c)removing about one-half of the fluid volume occupying the chamber byconveying platelet-poor component from the separation chamber to thereservoir, (d) rocking the separation chamber, with about one-half ofits fluid volume removed, to create intensified variable agitationforces within the separation chamber, (e) returning platelet-poorcomponent from the reservoir to the chamber, while rocking theseparation chamber, in a volume sufficient to essentially replace thefluid volume removed in step (c), to thereby at least partiallyresuspend platelet-rich concentrate within the separation chamber inresponse to the agitation forces, (f) conveying a partial volume ofplatelet-rich concentrate, resuspended in returned platelet-poorcomponent, from the separation chamber to a collection container,leaving a remaining volume of platelet-rich concentrate occupying theseparation chamber, and repeating steps (c) to (f) in succession untilsubstantially all of the platelet-rich concentrate is resuspended withabout 200 ml of returned platelet-poor component and conveyed to thecollection container.